Retailers have some catching up to do between now and Christmas — and it’s going to require a few markdowns.

Holiday sales are lagging expectations industrywide as tapped-out consumers have gone into hibernation after splurging on Black Friday deals.

Looking to stir shoppers, department stores and big-box chains have slashed prices on everything from cashmere sweaters to consumer electronics this month.

Yesterday, Gap’s Old Navy chain was advertising 50 percent off on all sweaters and hoodies. Last week, swanky stores including Bloomingdale’s, Neiman Marcus and Barneys were advertising discounts of more than half on designer clothing, shoes and handbags.

Nevertheless, experts say the discounts will have to get steeper for many chains to meet expectations this year. The final holiday stretch “is even more important than it has been over the last few years,” said Michael McNamara of MasterCard SpendingPulse.

Last year, retailers racked up $147 billion in sales during the 10 days leading up to Christmas — nearly 24 percent of the holiday season’s total, according to SpendingPulse. This year, that percentage will have to increase for Christmas to be called a success, according to many analysts.

“Super Saturday — the last Saturday before Christmas — is going to have to live up to its name,” McNamara said.

Evidence that retailers have recognized this reality began cropping up a week ago, when Macy’s announced its stores will be open for 48 hours straight in the two days leading up to Christmas Eve.

After controversially stretching their Black Friday hours into Thanksgiving this year, big chains, including Target, Walmart and Toys ‘R’ Us, are also expanding store hours in the final days before Christmas.

“It’s probably a necessary move to save the season,” says Britt Beemer of America’s Research Group. “But without the discounts and deals, it won’t work.”

As of last week, a mean of 64.9 percent of shoppers had completed their holiday purchases — well short of the 69.6 percent a year ago, according to the International Council of Shopping Centers.